In a mobile (cellular) communications network, (user) communication devices (also known as user equipment (UE), for example mobile telephones) communicate with remote servers or with other communication devices via base stations. In their communication with each other, communication devices and base stations use licensed radio frequencies, which are typically divided into frequency bands and/or time blocks.
In order to be able to communicate via the base stations, communication devices need to monitor control channels operated by the base stations. One of these control channels, the so-called physical downlink control channel (PDCCH) and/or the so-called evolved PDCCH (EPDCCH) in Rel-13, carries the scheduling assignments and other control information. The (E)PDCCH serves a variety of purposes. Primarily, it is used to convey the scheduling decisions to individual communication devices, i.e. scheduling assignments for uplink and downlink communication.
The information carried on the (E)PDCCH is referred to as downlink control information (DCI). Physical control channels, such as the (E)PDCCH, are transmitted on an aggregation of one or several consecutive control channel elements (CCEs), where a control channel element corresponds to nine resource element groups (REGs). Each REG has four resource elements (REs).
A paging channel is provided over (mapped to) the physical downlink shared channel (PDSCH) for notifying communication devices about a system information change and/or incoming communications for one or more communication devices (such as mobile terminated calls, short text messages, downlink data, and/or the like). Paging messages (although they are transmitted over the PDSCH) are scheduled via the (E)PDCCH. Specifically, in each radio frame transmitted by the base station there is at least one predetermined paging occasion (PO) (a maximum of four POs per radio frame), each PO being a subframe in which the base station may transmit control data over the PDCCH in order to schedule an associated paging message. Each paging message can identify one or more communication devices for which the paging message is sent. Whenever a PO includes a so-called paging identifier, i.e. a paging radio network temporary identifier (P-RNTI), which is the same for all LTE devices in the cell, each communication device processes the control data, and proceeds to decoding the paging message broadcast over the paging channel (at the time-frequency resource identified by the control data).
In more detail, whenever there is downlink data (or incoming call) for a particular communication device, the network notifies the base station(s) that may be serving that communication device about the data (or call). In response to this, the base station generates a radio resource control (RRC) paging message and transmits the generated paging message for the communication device (by broadcasting via the PDSCH). The paging message is scheduled using one of the predetermined POs, the location of which is known to the communication devices (e.g. from the base station's system information broadcast). The paging message includes one or more paging records identifying each communication device being paged and the reason for paging that communication device.
If a communication device finds the (E)PDCCH addressed by P-RNTI in (the control data sent via) the PO, then it proceeds to receiving and decoding the RRC paging message from the PDSCH resource block (RB) identified by the associated control data transmitted via the PDCCH PO. If a paging record is found for a particular communication device in the decoded RRC paging message, then that communication device proceeds to respond to the paging message (whilst other, non-paged, communication devices continue monitoring for the next PO). If appropriate, the paged communication device performs a random access procedure with the base station in order to establish a connection with the network and to be able to respond to the incoming communication that the paging message (i.e. the communication device's paging record) relates to.
Recent developments in telecommunications have seen a large increase in the use of machine-type communications (MTC) devices which are networked devices arranged to communicate and perform actions without human assistance. Examples of such devices include smart meters, which can be configured to perform measurements and relay these measurements to other devices via a telecommunication network. Machine-type communication devices are also known as machine-to-machine (M2M) communication devices.
MTC devices connect to the network (after performing an appropriate random access procedure, if necessary) whenever they have data to send to or receive from a remote ‘machine’ (e.g. a server) or user. MTC devices use communication protocols and standards that are optimised for mobile telephones or similar user equipment. However, MTC devices, once deployed, typically operate without requiring human supervision or interaction, and follow software instructions stored in an internal memory. MTC devices might also remain stationary and/or inactive for a long period of time. The specific network requirements to support MTC devices have been dealt with in the 3GPP technical specification (TS) 22.368 V13.1.0 the contents of which are incorporated herein by reference.
For the Release 13 (Rel-13) version of the standards relating to MTC devices, support for a reduced bandwidth of 1.4 MHz in downlink and uplink is envisaged. Thus, some MTC devices will support only a limited bandwidth (typically 1.4 MHz) compared to the total LTE bandwidth and/or they may have fewer/simplified components. This allows such ‘reduced bandwidth’ MTC devices to be made more economically compared to MTC devices supporting a larger bandwidth and/or having more complicated components. Beneficially, the EPDCCH is transmitted over a relatively narrow frequency spectrum (1.4 Mhz) that makes it compatible with Rel-13 reduced bandwidth MTC devices.
The lack of network coverage (e.g. when deployed indoors), in combination with the often limited functionality of MTC devices, can result in such MTC devices having a low data rate and therefore there is a risk of some messages or channels, such as the EPDCCH, not being received by an MTC device. In order to mitigate this risk, it has been proposed to increase the coverage of transmissions to support such MTC devices (e.g. corresponding to 20 dB for frequency division duplex (FDD) transmissions).
One approach proposed for the enhancement of coverage, for so-called ‘coverage enhanced MTC devices’, is the repetition of the same information (e.g. a DCI sent over the EPDCCH) across multiple subframes (e.g. two, three, or four subframes). In other words, for coverage enhanced (CE) MTC devices, the base station duplicates the transmitted information in the time domain (the base station re-transmits the same information in one or more subframes subsequent to the subframe in which that information is first sent). Such a coverage enhanced MTC device can be configured to combine the multiple copies of the (same) information received in the multiple subframes, and after combining the received information, the coverage enhanced MTC device is more likely to be able to decode the received information successfully than based on a single copy of the transmitted information. Similarly to the repetition of the same information by the base station, coverage enhanced MTC devices are also configured to duplicate (in the time domain) information transmitted to the base station to facilitate successful reception of that information at the base station.
In practice, MTC devices may be deployed in different locations and they may experience different channel conditions. Therefore, the number of repetitions may need to be tailored for each device's situation or coverage level, and each MTC device informs its serving base station of the amount of coverage required (e.g. 5 dB/10 dB/15 dB/20 dB coverage enhancement) to allow the base station to adjust its control signalling appropriately.
Paging messages are transmitted separately for MTC devices (e.g. low-complexity and/or coverage enhanced MTC devices) and for other (non-MTC) communication devices, such as conventional mobile telephones. Furthermore, 3GPP envisaged that paging messages for MTC devices may be transmitted in different subbands in dependence on the MTC device's mode of operation (e.g. whether it is operating in normal coverage mode (0 dB CE level), at 5 dB CE level, at 10 dB CE level, or at 15 dB CE level).